Nothing needs to be added.
Sure MP3 players and camera's are neat little additions but they aren't necessary for a GAMING platform.
What you need for a gaming platform is games so how about concentrating on them instead of adding rather minor improvements to what is already a fantastic package.

The upgrades from the original DS to the DS lite I can get behind but at some point you just have to kind of.. Stop.

Keep concentrating on games or if you're absolutely freaking insistant on putting out new hardware concentrate on making the DS2 or whatever instead of shoving unnecessary features onto this one.